Which are the major Emergency Notification Systems competitors for a large international company?

I work for a technology management and consulting services firm with 201-500 employees. 

Who do you see as the major competitors in ENS for a large international company?
I have received information from or am awaiting the response from EverBridge, Aurea, Regroup, OnSolve. Do you have experience with any of these solutions or can recommend any others to consider?

Thanks! I appreciate the help.